Other data, from temperature data to CO2 atmospheric data, to ozone data, shows that the current change has been the fastest for the last ~400 thousand years.
I found an interesting article (and not by crackpots) on the history of rapid climate change at the below website. I don’t think that the rate of change we are experiencing now is as fast as has been seen to occur in the past, based on ice cores from Greenland and backed up with other data (note the underlined sentence below). Let me caveat that with this: That does not mean that humans are not responsible for climatic change, indeed, scientists are worried that small perturbations of the system could cause a rapid shift in temperature. I did find another article, however, that showed just how much change has been made in the last 40 or so years in CO2 concentrations, and the change is not great…maybe 2.5 parts per million…if there are any climatic scientists out there, I would be curious if a change in CO2 concentrations of that magnitude had ever been correlated in the past with climate change.
http://www.aip.org/history/climate/rapid.htm
Swings of temperature that scientists in the 1950s believed to take tens of thousands of years, in the 1970s to take thousands of years, and in the 1980s to take hundreds of years, were now found to take only decades. Ice core analysis by Dansgaard's group, confirmed by the Americans' parallel hole, showed rapid oscillations of temperature repeatedly at irregular intervals throughout the last glacial period. ***<u>Greenland had sometimes warmed a shocking 7°C within a span of less than 50 years.</u>*** For one group of American scientists on the ice in Greenland, the "moment of truth” struck on a single day in midsummer 1992 as they analyzed a cylinder of ice, recently emerged from the drill hole, that came from the last years of the Younger Dryas. They saw an obvious change in the ice, visible within three snow layers, that is, scarcely three years! The team analyzing the ice was first excited, then sobered — their view of how climate could change had shifted irrevocably. The European team reported seeing a similar step within at most five years. "The general circulation in the Northern Hemisphere must have shifted dramatically," Dansgaard’s group eventually concluded.<u>(56*)</u> The record of dust found in the ice certainly suggested that a wide region had been involved, but might the change have been restricted to parts of the world near Greenland? The first hints of the answer came from oceanographers, who had been hunting out seabed zones where bioturbation by burrowing worms did not smear any record of rapid change. In some places the sediments accumulated very rapidly, while in others, the seawater lacked enough oxygen to sustain life. The first results, from the Norwegian Sea in 1992, confirmed that the abrupt changes seen in Greenland ice cores were not confined to Greenland alone. Later work on seabed cores from the California coast to the Arabian Sea, and on chemical changes recorded in cave stalagmites from Switzerland to China, confirmed that the oscillations found in the Greenland ice had been felt throughout the Northern Hemisphere. Meanwhile, in the late 1980s and early 1990s, improved carbon-14 techniques gave the first accurate dates for sediments containing pollen and other carbon-bearing materials at locations ranging from Japan to Tierra del Fuego. Good dates finally allowed correlation of many geological records with the Greenland ice. The results suggested that the Younger Dryas events had affected climates around the world. The extent and nature of the perturbation was controversial. But scientists were increasingly persuaded that abrupt climate shifts could have global scope, even if they affected different places differently — colder here and warmer there, wetter here and drier there.<u>(57)</u> Could such drastic variations happen not only during glacial times, but also in warm periods like the present? That was the most interesting question in 1992, as the European drillers penetrated clear through the last glacial epoch to the preceding "Eemian" period, more than 100,000 years back — a time similar to our own, or even warmer. There, too, they saw dramatic shifts. However, further analysis cast that into doubt. The layers from the Eemian warm period were down near bedrock, distorted by ice flow. Comparison of the two groups' cores gave divergent results. Again scientists had benefitted from drilling parallel cores. But this time the lesson, valuable if unwelcome, was that they must do more work.